1. Field of the Invention
The present invention relates to the manufacturing of semiconductor devices. More particularly, the present invention relates to a chuck plate of a chuck assembly of ashing equipment for removing photoresist from the surface of a wafer after an etching process is performed using the photoresist as a mask.
2. Description of the Related Art
Semiconductor devices are made, in part, by removing portions of a semiconductor wafer. These portions of the wafer are exposed by a patterned photoresist, and the exposed portions are then removed by etching. Plasma etching is the main etching process used. In plasma etching, a process gas is transformed into a plasma. The plasma reacts with the portions of the wafer to thereby remove such portions.
A polymer is produced as a by-product of the reaction. The by-product, namely, the polymer, is in the form of a vapor. Accordingly, the polymer is deposited on all of the inner surfaces of the etching chamber as well as on a portion a lower surface of the wafer without any selectivity.
As shown in FIG. 1, the polymer Pxe2x80x2 is generally formed on the lower surface of the wafer W in a region d of a width of about 8xcx9c10 mm extending inwardly from the edge of the wafer W. Consequently, the lower surface of the wafer W adheres to a cathode that is used to execute the plasma etching process. Meanwhile, as shown in FIG. 3, once the wafer W has been etched, the photoresist (PR) is removed from the wafer W through a stripping or ashing procedure. The wafer is then cleaned to remove any PR residue and/or other types of particles that have accumulated on the wafer.
The ashing process for removing the PR from the wafer W is performed by ashing equipment 10, as shown in FIG. 2. First, the wafer W is transferred into an airtight chamber 12 through the door unit 14. The wafer W is supported by a chuck plate 18 of a chuck assembly 16. Then ashing gas G, such as oxygen O2 and nitrogen N2 or the like, is excited by high frequency power so as to assume a plasma state, namely, an ion (radical) state. The plasma is supplied into the airtight chamber 12 via an upper gas supplying unit 22.
The wafer is heated, and under this condition, the ashing gas G in the state of plasma reacts with the PR, and the reaction removes the PR and forms the polymer Pxe2x80x2 vapor. The vapor is discharged through an exhaust pipe 24 connected to a vacuum pressure forming unit (not shown). However, as mentioned above, some of the vapor solidifies on the lower surface of the wafer W. In this case, the polymer Pxe2x80x2 adheres to an upper surface of the chuck plate 18. Thus, it becomes difficult to foster the reaction between the plasma and the PR. Furthermore, heat is conducted from a lower part 20 of the heater through the chuck plate 18. This heat burns a component of the polymer Pxe2x80x2, such as the PR component. The carbon produced as a result contaminates the chuck plate 18 and the wafer W.
Still further, although the polymer Pxe2x80x2 existing on the lower surface of the wafer W is subjected to the cleaning process after the etching process is completed, the polymer Pxe2x80x2 is not readily removed by such process. Thus, the presence of the polymer Pxe2x80x2 prolongs the cleaning process. Furthermore, if the next process is executed without removing the polymer Pxe2x80x2, the polymer Pxe2x80x2 can give rise to defects that lower the production yield.
Accordingly, an object of the present invention is to substantially obviate one or more of the limitations and disadvantages of the related art.
More specifically, the primary object of the present invention is to reduce the time necessary for cleaning ashing equipment after the equipment has been used to etch away photoresist from a wafer, and to prevent the etching process from creating defects that would otherwise adversely impact the subsequent processing of the wafer, whereby the manufacturing yield is improved.
To achieve these objects, the present invention provides a chuck plate, and a chuck assembly comprising the same, that facilitate the removal of polymer from the lower surface of a wafer during the time photoresist is being plasma etched from the upper surface of the wafer. The chuck plate has a central supporting part whose upper surface is horizontal so as to support the bottom surface of a wafer, and a stepped part extending radially outwardly from the supporting part and having an upper surface disposed at a level below the upper surface of the supporting part. The upper surface of the stepped part is designed to support the bottom surface of the wafer except for an outer peripheral portion thereof that includes the polymer formation region.
To this end, the upper surface of the supporting part has an outer shape corresponding to but smaller than that of the wafer, including the so-called flat zone of the wafer. Alternatively, the outer shape of the upper surface of the supporting part is circular and has a radius smaller than the radius of curvature of the arcuate portion of the outer edge of the wafer.
Preferably, the upper surface of the supporting part and the upper surface of the stepped part are vertically spaced from one another by 0.3xcx9c0.5 mm. Also, the upper surface of the stepped part extends radially outwardly to at least the axial projection of the outer peripheral edge of the wafer. The heater of the chuck plate assembly can therefore extend beneath the stepped part so as to transfer heat to the polymer formation region that overhangs the supporting part so as to be disposed above the upper surface of the stepped part.
Furthermore, the chuck plate may have an outermost peripheral part forming a protrusion that extends upwardly beyond the upper surface of the stepped part. The protrusion may have may extend beyond the plane of the horizontal upper surface of the support part and may have an inclined inner side surface so as to serve as a guide when the wafer is lowered onto the chuck plate.
The inner side surface of the protrusion may have a sectional shape, in a horizontal plane, corresponding to that of the outer edge of the upper surface of the supporting part, i.e., may have a horizontal sectional shape corresponding to that of the wafer or one that is circular. In the latter case, the outer edge of the upper surface of the supporting part and the inner side surface of the protrusion are positioned relative to one another so as to accommodate the entire outer peripheral edge of the wafer therebetween.
Based on the fact that a polymer will typically form over 8xcx9c10 mm of the outer peripheral region of the bottom surface of the wafer, the inner side surface of the protrusion is designed to be spaced from the outer peripheral edge of the wafer by 0.5xcx9c1.5 mm. Furthermore, the outer edge of the upper surface of the supporting part and the inner side surface of the protrusion are preferably spaced horizontally across from one another by 10.5 xcx9c12.5 mm.
In accordance with the present invention, ashing gas injected into the process chamber of the ashing equipment in the state of plasma can flow into an opening defined between the upper surface of the stepped part of the chuck plate and the polymer formation region of the bottom surface of the wafer. The plasma reacts with the polymer thereby vaporizing the same. As a result, the photoresist and the polymer are simultaneously removed from the wafer.